Lash adjuster

ABSTRACT

A lash adjuster is provided of which the adjusting screw can be repeatedly and easily brought into the initial set position. 
     In a lash adjuster including a nut member  14  having an internal thread  20  on the inner periphery thereof, an adjusting screw  15  having an external thread  19  on the outer periphery thereof that is in threaded engagement with the internal thread  20,  and a return spring  17  biasing the adjusting screw  15  in the direction to protrude from the nut member  14,  a washer  18  is provided which is axially deformed and produces frictional resistance to rotation that serves to prevent rotation of the adjusting screw  15  by its elastic restoring force when the adjusting screw  15  is threaded into the nut member  14.

TECHNICAL FIELD

This invention relates to a lash adjuster mounted in a valve gear of an engine.

BACKGROUND ART

Known valve gears for moving a valve provided at an intake port or an exhaust port of an engine include one including an arm pivotable about one end thereof and adapted to be pushed down by a cam at its central portion, thereby pushing down the valve stem at its other end (swing arm type valve gear), one including an arm pivotable about its central portion and adapted to be pushed up by a cam at its one end, thereby pushing down a valve stem at its other end (rocker arm type valve gear), and one including a vertically slidable lifter body adapted to be pushed down by a cam, thereby pushing down a valve stem (direct type valve gear).

With these valve gears, when gaps change between various component parts of the valve gear due to differences in thermal expansion coefficient between these component parts during operation of the engine, such gaps may cause noise and compression leakage. Gaps may also change between sliding parts of the valve gear due to wear of these parts, thus producing noise.

In order to prevent such noise and compression leakage, a lash adjuster is mounted in an ordinary valve gear to absorb any gap between component parts of the valve gear.

Among known lash adjusters for swing arm type valve gears, there is one comprising a nut member received in a receiving hole formed in the top surface of a cylinder head, an adjusting screw having an external thread on the outer periphery thereof that is in threaded engagement with an internal thread formed on the inner periphery of the nut member, and a return spring biasing the adjusting screw in the direction to protrude upwardly from the nut member, whereby the arm of the valve gear is supported by the end of the adjusting screw protruding from the nut member (Patent document 1).

For use in a rocker arm type valve gear, a lash adjuster is known which comprises a nut member received in a receiving hole formed in the bottom surface of an arm that pivots with the rotation of a cam, an adjusting screw having an external thread on the outer periphery thereof that is in threaded engagement with an internal thread formed on the inner periphery of the nut member, and a return spring biasing the adjusting screw in the direction to protrude downwardly from the nut member, whereby the valve stem of the valve gear is pressed by the end of the adjusting screw protruding from the nut member (Patent document 2).

For use in a direct type valve gear, there is known a lash adjuster comprising a lifter body vertically slidably inserted in a guide hole formed in a cylinder head, a nut member vertically movable together with the lifter body, an adjusting screw having an external thread on its outer periphery that is in threaded engagement with an internal thread formed on the inner periphery of the nut member, and a return spring biasing the adjusting screw in the direction to protrude downwardly from the nut member, whereby the valve stem of the valve gear is pressed by the end of the adjusting screw protruding from the nut member (Patent document 3).

With these lash adjusters, when gaps between component parts of the valve gear change due e.g. to thermal expansion of the valve gear, the adjusting screw moves axially while rotating in the nut member according to the change in the gaps, thereby adjusting the gaps between the component parts of the valve gear.

While these adjusters are not mounted to a valve gear, the adjusting screw protrudes from the nut member under the biasing force of the return spring. If these lash adjusters are mounted on the valve gear in this state, the valve cannot be seated on the vale seat, thus making complete combustion of the engine impossible. Thus, when mounting these lash adjusters on a valve gear, it is necessary to thread the adjusting screw into the nut member and keep pressing it so as not to protrude from the nut member. It is however troublesome to keep pressing the adjusting screw.

In order to keep the adjusting screw in the position where the adjusting screw is threaded into the nut member (hereinafter referred to as “initial set position”), it is proposed, in a lash adjuster for a direct type valve gear, to fill the gap between the adjusting screw and the nut member with wax which serves to prevent the adjusting screw from turning (Patent document 3).

With this lash adjuster, since the wax prevents the adjuster screw form turning, it is not necessary to keep pressing the adjusting screw when mounting the lash adjuster on the valve gear. After the lash adjuster has been mounted on the vale gear, the wax melts due to a rise in temperature during operation of the engine, thus releasing the initial set position.

But once the wax between the adjusting screw and the nut member melts, it flows out of the space between the adjusting screw and the nut member, thus making it impossible to move the adjusting screw into the initial set position and keep it in this position again, when e.g. overhauling the engine. This is inconvenient.

Thus, a lash adjuster for a direct type valve gear is proposed which makes it possible to repeatedly move and keep the adjusting screw in the initial set position by inserting a set pin into small-diameter through holes formed in the adjusting screw and the nut member, thereby preventing turning of the adjusting screw (Patent document 4).

But this solution is costly because the small-diameter holes have to be formed in the adjusting screw and the nut member. Also, to keep the adjusting screw in the initial set position, it is necessary to align the through hole formed in the adjusting screw with the through hole formed in the nut member. Aligning such small-diameter holes with each other is not easy.

Also, there is the possibility that an operator may forget to pull out the set pin when this lash adjuster has been mounted to the valve gear. Even if the operator pulls out the set pin, the operator may leave the set pin in the engine. Also, since the set is used again when overhauling the engine, it is necessary to keep the set pin until then, which is troublesome.

-   Patent document 1: JP patent publication 2005-248912A -   Patent document 2: JP patent publication 2007-92668A -   Patent document 3 JP patent publication 2000-110523A -   Patent document 4: JP patent publication 11-62519A

DISCLOSURE OF THE INVENTION Object of the Invention

An object of the invention is to provide a lash adjuster of which the adjusting screw can be repeatedly and easily brought into the initial set position, and which can be handled easily after having been mounted to a valve gear.

Means to Achieve the Object

In order to achieve this object, the prevent invention provides a lash adjuster including an initial setting means configured to be deformed in an axial direction when the adjusting screw is threaded into the nut member, thereby producing frictional resistance to rotation that tends to prevent rotation of the adjusting screw due to an elastic restoring force of the initial setting means.

With this arrangement, the frictional resistance to rotation produced when the adjusting screw is threaded into the nut member prevents rotation of the adjusting screw, thereby keeping the adjusting screw in the initial set position.

The initial setting means is preferably configured to produce the elastic restoring force so as to be symmetrical with respect to the axis so that the adjusting screw is less likely to incline in the initial set position.

The initial setting means may be an elastic member located so as to oppose an end of the adjusting screw that is inserted in the nut member. With this arrangement, when the adjusting screw is threaded into the nut member, the elastic member located so as to oppose the end of the adjusting screw inserted in the nut member is compressed from up and down by the adjusting screw and the closed end of the nut member, thus producing frictional resistance to rotation between the adjusting screw and the elastic member due to the elastic restoring force of the elastic member. The frictional resistance to rotation thus produced prevents rotation of the adjusting screw, thereby keeping the adjusting screw in the initial set position. The initial set position of the adjusting screw can be released by applying an impact load to the adjusting screw.

The elastic member may be a washer comprising an annular sheet having circumferentially extending spring pieces formed by cutting and raising portions of the annular sheet. This washer can be compressed more markedly than other washers, so that if unintended vibrations or impacts are applied to the adjusting screw, the initial set position of the adjusting screw is less likely to be released, which makes it possible to transport the lash adjuster more safely.

By cutting and raising the spring pieces in a direction to bias the adjusting screw in the loosening direction, when an impact load is applied to the adjusting screw in the initial set position, the adjusting screw can more easily protrude from the nut member while rotating, which in turn makes it possible to reliably release the initial set position of the adjusting screw by cranking the engine. The washer may be formed by pressing spring steel.

Also, the elastic member may be a toothed washer comprising an annular sheet and teeth radially extending from the annular sheet. In this case, the teeth of the toothed washer are preferably twisted in a direction to bias the adjusting screw in the loosening direction. The toothed washer may be formed by pressing spring steel.

The elastic member may also be a conical spring washer, a corrugated spring washer, or a spring washer.

The adjusting screw may include a head protruding from the nut member and having an outer diameter larger than the inner diameter of the nut member, whereby said adjusting screw serves as the initial setting means.

With this arrangement, when the adjusting screw is threaded into the nut member, since the portion of the adjusting screw located in the nut member is pulled axially into the nut member, with its head supported on the nut member, the adjusting screw is pulled axially and deformed. This produces frictional resistance to rotation between the head and the nut member due to the elastic restoring force of the adjusting screw. The frictional resistance to rotation thus produced prevents rotation of the adjusting screw in the initial set position. The state in which the adjusting screw is prevented from rotating can be released by applying an impact load to the adjusting screw.

The adjusting screw may have a tapered surface formed on its portion protruding from the nut member, and configured to be brought into contact with a tapered surface formed on the nut member when the adjusting screw is threaded into the nut member, thereby producing the frictional resistance to rotation. With this arrangement, when the adjusting screw is threaded into the nut member, the tapered surfaces contact each other, and a large frictional force is produced between the tapered surfaces due to the wedging effect of the tapered surfaces, which makes it possible to reliably prevent rotation of the adjusting screw.

The adjusting screw and the nut member may be degreased to more reliably prevent rotation of the adjusting screw.

The initial setting means may be an annular member engaged in a circumferential groove formed in an outer periphery of a portion of the adjusting screw protruding from the nut member and having an outer diameter larger than the inner diameter of the nut member.

With this arrangement, when the adjusting screw is threaded into the nut member, the annular member engaged in the circumferential groove formed in the outer periphery of the adjusting screw is pressed by the top end surface of the nut member and deformed. This produces frictional resistance to rotation between the annular member and the nut member due to the elastic restoring force of the annular member. The frictional resistance to rotation thus produced prevents rotation of the adjusting screw, thus keeping the adjusting screw in the initial set position. The state in which the adjusting screw is prevented from rotating can be released by applying an impact load to the adjusting screw.

The annular member may be an O-ring made of rubber, or a ring made of an elastic resin. With this arrangement, since the annular member is deformed markedly when the adjusting screw is threaded into the nut member, it is possible to control the frictional resistance to rotation applied to the annular member by adjusting the axial displacement of the adjusting screw. Also, by creating a gap between the initial setting member and the nut member, the initial set position of the adjusting screw can be released. By using an O-ring as an elastic member, the lash adjuster can be manufactured at a lower cost because O-rings are widely commercially available.

The annular member may be a conical coil spring. Preferably, such a conical coil spring has a small-diameter end engaged in the circumferential groove with a radial interference fit. With this arrangement, since there will be no backlash between the cylindrical coil spring and the adjusting screw, the position of the cylindrical coil spring stabilizes. This in turn makes it possible to accurately control the frictional resistance to rotation produced between the conical coil spring and the nut member when bringing the adjusting screw to the initial set position, by adjusting the axial displacement of the adjusting screw.

The annular member may be a cylindrical coil spring comprising two coil windings. Preferably, such a coil spring is engaged in the circumferential groove with a radial interference fit. With this arrangement, since there will be no backlash between the conical coil spring and the adjusting screw, the position of the conical coil spring stabilizes. This in turn makes it possible to accurately control the frictional resistance to rotation produced between the conical coil spring and the nut member when bringing the adjusting screw to the initial set position, by adjusting the axial displacement of the adjusting screw.

The above-mentioned arrangements are applicable e.g. to the following lash adjusters.

1) A lash adjuster for a swing arm type valve gear wherein the nut member is inserted in a receiving hole formed in a top surfaced of a cylinder head, and wherein the adjusting screw has a portion protruding from the nut member and pivotally supporting an arm of the valve gear. 2) A lash adjuster for a rocker arm type valve gear wherein the nut member is inserted in a receiving hole formed in a bottom surface of an arm which pivots with the rotation of a cam, and wherein the adjusting screw has an end protruding from the nut member and pressing a valve stem of the valve gear. 3) A lash adjuster for a direct type valve gear wherein the nut member is configured to vertically move together with a lifter body vertically slidably inserted in a guide hole formed in a cylinder head, and wherein the adjusting screw has an end protruding from the nut member and pressing a valve stem of a valve gear.

Further, the lash adjusters 1) and 2) above may have the following configurations too.

The annular member may be a cocoon-shaped clip comprising two C-shaped annular portions having different centers and coupled together, one of said two C-shaped annular portions being corrugated in the axial direction, and wherein said cocoon-shaped clip is slidable between a position where said one C-shaped annular portion is engaged in the circumferential groove and a position where the other C-shaped annular portion is engaged in the circumferential groove.

With this arrangement, with the corrugated C-shaped annular portion engaged in the circumferential groove, when the adjusting screw is threaded into the nut member, the corrugated C-shaped annular portion is pressed by the nut member and deformed, which produces frictional resistance to rotation between the C-shaped annular portion and the nut member due to the elastic restoring force of the C-shaped annular portion. The frictional resistance to rotation thus produced prevents rotation of the adjusting screw, thus keeping the adjusting screw in the initial set position. The initial set position of the adjusting screw can be released by sliding the cocoon-shaped clip until the corrugated C-shaped annular portion is disengaged.

The C-shaped annular portions may be circular or polygonal.

The annular member may be a set clip comprising a C-shaped annular portion engaged in the circumferential groove with a radial interference fit, and a pair of resetting tabs extending from two ends of the C-shaped annular portion, respectively.

With this arrangement, when the adjusting screw is threaded into the nut member, the C-shaped annular portion of the set clip is pressed against the nut member, so that the adjusting screw is kept in the initial set position by the frictional resistance to rotation produced between the C-shaped annular portion and the nut member 14. In this state, when the C-shaped annular portion is radially expanded by operating the resetting tabs, thereby causing the C-shaped annular portion and the nut member to slip relative to each other, since the friction coefficient between the C-shaped annular portion and the nut member changes from a static friction coefficient to a dynamic friction coefficient, the initial set position of the adjusting screw can be is released.

Preferably, the C-shaped annular portion is corrugated in the axial direction. With this arrangement, when the adjusting screw is threaded into the nut member, the C-shaped annular portion is pressed against the nut member and deformed, thus producing frictional resistance to rotation corresponding to the amount of deformation. This makes it possible to control the frictional resistance to rotation by adjusting the axial displacement of the adjusting screw.

The conical coil spring may have a large-diameter end, and includes a resetting tab radially outwardly extending from the large-diameter end. In this case, by raising the resetting tab, thereby forming a gap between the conical coil spring and the nut member, the initial set position of the adjusting screw can be is released. By circumferentially moving the resetting tab, thereby causing the conical coil spring and the nut member to slip relative to each other, too, since the friction coefficient between the conical coil spring and the nut member changes from a static friction coefficient to a dynamic friction coefficient (which is smaller than a static friction coefficient), it is possible to release the initial set position of the adjusting screw. While the initial set position of the adjusting screw can be released by applying an impact load to the adjusting screw, too, the initial set position can be released more reliably by operating the resetting tab.

The cylindrical coil spring may include a resetting tab radially outwardly extending from one end thereof. In this case, by circumferentially moving the resetting tab, thereby causing the cylindrical coil spring and the nut member to slip relative to each other, since the friction coefficient between the cylindrical coil spring and the nut member changes from a static friction coefficient to a dynamic friction coefficient, it is possible to release the initial set position of the adjusting screw.

Preferably, the resetting tab extending from one end of the C-shaped annular portion crosses the resetting tab extending from the other end of the C-shaped annular portion. With this arrangement, by pressing the pair of resetting tabs from outside to narrow the distance therebetween, the C-shaped annular portion can be radially expanded, so that the initial set position of the adjusting screw can be more easily released than with the lash adjuster of the type in which the C-shaped annular portion is radially expanded by increasing the distance between the resetting tabs.

Advantages of the Invention

With the lash adjuster according to the present invention, the adjusting screw is kept in the initial set position using the frictional resistance to rotation produced when the adjusting screw is threaded into the nut member, the adjusting screw can be repeatedly moved into and kept in the initial set position.

Also, with this lash adjuster, since the adjusting screw can be brought into the initial set position simply by threading the adjusting screw into the nut member, the adjusting screw can be brought into the initial set position more simply than with a lash adjuster in which the initial setting means has to be fitted after threading the adjusting screw into the nut member.

With this lash adjuster, when the camshaft is rotated with the lash adjuster mounted on the valve gear, the initial set position is automatically released by an impact load applied to the adjusting screw. Thus, an operator does not have to remember to release the initial set position of the adjusting screw when the lash adjuster is mounted on the valve gear.

With this lash adjuster, after the initial set position of the adjusting screw has been released, the elastic member is retained in the lash adjuster. Thus, there is no possibility of inadvertently leaving such a separate member in the engine when the initial set position of the adjusting screw is released. Also, there is no need to keep a separate member such as a set pin in stock after the lash adjuster 1 has been mounted in the valve gear in preparation for overhaul.

The lash adjuster is inexpensive because there is no need to form holes for inserting the set pin in the adjusting screw and the nut member.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of valve gear in which is mounted a lash adjuster according to a first embodiment of the present invention.

FIG. 2 is an enlarged sectional view of and around an adjusting screw shown in FIG. 1, showing how the adjusting screw is brought into its initial set position.

FIG. 3 is an enlarged sectional view showing the initial set position of the adjusting screw.

FIG. 4 is a sectional view taken along line IV-IV of FIG. 2.

FIG. 5 is an enlarged perspective view of a washer shown in FIG. 2.

FIG. 6 is a front view showing a state in which the initial set position of the adjusting screw shown in FIG. 1 has been released.

FIG. 7( a) is a plan view of a toothed washer as an alternative example of the washer of FIG. 5; and FIG. 7( b) is a side view of the toothed washer shown in FIG. 7( a).

FIG. 8 is a front view of a valve gear in which is mounted a lash adjuster according to a second embodiment of the present invention.

FIG. 9 is an enlarged sectional view of and around an adjusting screw shown in FIG. 8, showing the state before the adjusting screw is brought into its initial set position.

FIG. 10 is an enlarged sectional view showing the initial set position of the adjusting screw of FIG. 9.

FIG. 11( a) is a plan view of a toothed washer shown in FIG. 9; and FIG. 11(b) is a sectional view of the toothed washer shown in FIG. 11( a).

FIG. 12 is a front view of valve gear in which is mounted a lash adjuster according to a third embodiment of the present invention.

FIG. 13 is an enlarged sectional view of and around an adjusting screw shown in FIG. 12, showing the state before the adjusting screw is brought into its initial set position.

FIG. 14 is an enlarged sectional view showing the initial set position of the adjusting screw of FIG. 13.

FIG. 15 is an enlarged sectional view of and around the adjusting screw of a lash adjuster according to a fourth embodiment of the present invention, showing how the adjusting screw is brought into its initial set position.

FIG. 16 is a front view of a valve gear, showing the state in which the initial set position of the adjusting screw shown in FIG. 15 has been released.

FIG. 17 is an enlarged sectional view of and around the adjusting screw of a lash adjuster according to a fifth embodiment of the present invention, showing how the adjusting screw is brought into its initial set position.

FIG. 18 is a front view of a valve gear, showing the state in which the initial set position of the adjusting screw shown in FIG. 17 has been released.

FIG. 19 is an enlarged sectional view of and around the adjusting screw of a lash adjuster according to a sixth embodiment of the present invention, showing how the adjusting screw is brought into its initial set position.

FIG. 20 is a front view of valve gear in which is mounted a lash adjuster according to a seventh embodiment of the present invention.

FIG. 21 is an enlarged sectional view of and around an adjusting screw shown in FIG. 20, showing how the adjusting screw is brought into its initial set position.

FIG. 22 is an enlarged sectional view showing the initial set position of the adjusting screw of FIG. 21.

FIG. 23 is an enlarged sectional view showing the state in which the initial set position of the adjusting screw shown in FIG. 20 has been released.

FIG. 24 is an enlarged sectional view of a modification of the lash adjuster shown in FIG. 20.

FIG. 25 is an enlarged sectional view of an adjusting screw shown in FIG. 24.

FIG. 26 is an enlarged sectional view of a modification of the lash adjuster shown in FIG. 22.

FIG. 27 is a sectional view taken along line XXVII-XXVII of FIG. 26.

FIG. 28 is an enlarged sectional view showing the initial set position of an adjusting screw shown in FIG. 26.

FIG. 29 is an enlarged sectional view of a modification of the lash adjuster shown in FIG. 22.

FIG. 30 is sectional view taken along line XXX-XXX of FIG. 29.

FIG. 31 is an enlarged sectional view showing the initial set position of an adjusting screw shown in FIG. 29.

FIG. 32 is an enlarged sectional view taken along of a modification of the lash adjuster shown in FIG. 22.

FIG. 33 is a sectional view taken along line XXXIII-XXXIII of FIG. 32.

FIG. 34 is an enlarged sectional view showing the initial set position of an adjusting screw shown in FIG. 32.

FIG. 35 is an enlarged sectional view of a modification of the lash adjuster shown in FIG. 29.

FIG. 36 is a sectional view taken along line XXXVI-XXXVI of FIG. 35.

FIG. 37 is an enlarged sectional view of a modification of the lash adjuster shown in FIG. 22.

FIG. 38 is a sectional view taken along line XXXVIII-XXXVIII of FIG. 37.

FIG. 39 is a sectional view of the lash adjuster, showing the state in which the initial set position of an adjusting screw shown in FIG. 38 has been released.

FIG. 40 is an enlarged sectional view of a modification of the lash adjuster shown in FIG. 38.

FIG. 41 is a sectional view of the lash adjuster, showing the state in which the initial set position of an adjusting screw shown in FIG. 40 has been released.

FIG. 42 is an enlarged sectional view of a lash adjuster according to an eighth embodiment of the present invention, showing the state in which its adjusting screw protrudes from the nut member.

FIG. 43 is an enlarged sectional view showing the initial set position of the adjusting screw shown in FIG. 42.

FIG. 44 is an enlarged sectional view of a modification of the lash adjuster shown in FIG. 42.

FIG. 45 is an enlarged sectional view showing the initial set position of an adjusting screw shown in FIG. 44.

FIG. 46 is an enlarged sectional view of a modification of the lash adjuster shown in FIG. 42.

FIG. 47 is an enlarged sectional view showing the initial set position of an adjusting screw shown in FIG. 46.

FIG. 48 is an enlarged sectional view of a lash adjuster according to a ninth embodiment of the present invention, showing the initial set position of its adjusting screw.

DESCRIPTION OF THE NUMERALS

-   2. Cylinder head -   6. Arm -   13. Receiving hole -   14. Nut member -   15. Adjusting screw -   17. Return spring -   18. Washer -   19. External thread -   20. Internal thread -   24. Protruding end -   26. Spring piece -   27. Tooth -   28. Toothed washer -   32. Cylinder head -   35. Valve stem -   39. Guide hole -   40. Lifter body -   41. Nut member -   44. Adjusting screw -   65. Valve stem -   67. Arm -   73. Cam -   74. Nut member -   75. Adjusting screw -   77. Receiving hole -   91. Head -   92. Tapered surface -   93. Tapered surface -   121. Circumferential groove -   122. O-ring -   123. Conical coil spring -   124. Resetting tab -   126. Cylindrical coil spring -   127. Resetting tab -   128. Set clip -   129. C-shaped annular portion -   130. Pair of resetting tabs -   132. Cocoon-shaped clip -   133. C-shaped annular portion -   134. C-shaped annular portion

BEST MODE FOR EMBODYING THE INVENTION

FIG. 1 shows a valve gear including a lash adjuster according to a first embodiment of the present invention. This valve gear includes a valve 4 disposed at an intake port 3 of a cylinder head 2 of an engine, a valve stem 5 connected to the valve 4, and an arm 6 pivotally supported by the lash adjuster 1.

The valve stem 5 extends upwardly from the valve 4 and slidably extends through the cylinder head 2. An annular spring retainer 7 is fixed around the valve stem 5 at its top end portion. A valve spring 8 is mounted between the bottom surface of the spring retainer 7 and the top surface of the cylinder head 2. The valve spring biases the valve stem 5 upwardly through the spring retainer 7, thereby seating the valve 4 on a valve seat 9.

The arm 6 has its one end supported by the lash adjuster 1, and the other end in contact with the top end of the valve stem 5. A roller 11 is mounted to the arm 6 at its mid-portion so as to be brought into contact with a cam 10 provided over the arm 6. The cam 10 is integrally formed on a camshaft 12 which rotates in unison with an engine crankshaft (not shown) so that when the camshaft 12 rotates, the arm 6 is pushed down by a cam lobe 10 b which bulges from a base circle 10 a.

The lash adjuster 1 is received in a receiving hole 13 formed in the top surface of the cylinder head 2. As shown in FIG. 2, the lash adjuster 1 includes a cylindrical nut member 14 having an open top end, an adjusting screw 15 inserted in the nut member 14, a bottom member 16 closing the bottom end of the nut member 14, a return spring 17 mounted between the bottom member 16 and the adjusting screw 15, and a washer 18 mounted in the nut member 14.

An external thread 19 is formed on the outer periphery of the adjusting screw 15 at its bottom end portion, and is in threaded engagement with an internal thread 20 formed on the inner periphery of the nut member 14. The external thread 19 and the internal thread 20 both have a pressure flank 21 for receiving pressure when a load is applied to the adjusting screw 15 that tends to push the adjusting screw 15 into the nut member 14, and a clearance flank 22, with the pressure flank having a larger flank angle than the clearance flank, so that the threads 19 and 20 have a serration-shaped longitudinal section. With this arrangement, when a static load is applied to the adjusting screw 15 that tends to push in the adjusting screw, the rotation of the adjusting screw 15 is prevented due to the frictional resistance between the pressure flanks 21 of the external thread 19 and the internal thread 20. On the other hand, when a static load is applied to the adjusting screw 15 that tends to push out the adjusting screw, slip occurs between the clearance flanks 22 of the external thread 19 and the internal thread 20, thus allowing rotation of the adjusting screw 15. The external thread 19 and the internal thread 20 may have a pressure flank 21 having a flank angle of 75° and a clearance flank 22 having a flank angle of 15°.

The return spring 17 has its bottom end supported on the bottom member 16, and the top end pressed against the adjusting screw 15 through a spring seat 23, thereby biasing the adjusting screw 15 in a direction to protrude upwardly from the nut member 14.

The adjusting screw 15 has a hemispherical protruding end 24. As shown in FIG. 1, the protruding end 24 is engaged in a recess 25 formed in the bottom surface of the arm 6, thus supporting the arm 6 so as to be pivotable about the recess 25.

As shown in FIGS. 2 and 4, the washer 18 is an annular member provided between the adjusting screw 15 and the bottom member 16 so as to face the end of the adjusting screw 15 located in the nut member and surround the return spring 17. As shown in FIG. 5, the washer 18 is an annular sheet having circumferentially extending spring pieces 26 formed by partially cutting and raising the annular sheet at equal angular intervals. As shown in FIG. 5, the washer 18 is structured such that the spring pieces 26 are sandwiched between the adjusting screw 15 and the bottom member 16 when the adjusting screw 15 is threaded into the nut member 14. As seen from the adjusting screw 15, the spring pieces 26 are raised toward the adjusting screw such that the spring pieces 26 bias the adjusting screw 15 in the loosening direction (which means that if the external thread 19 is a right-hand twist, each spring piece 26 extends counterclockwise from its proximal to distal ends, as seen from the adjusting screw 15). The washer 18 can be formed by pressing a spring steel material.

This lash adjuster 1 is assembled into the valve gear e.g. in the following manner.

First, as shown by the arrow in FIG. 2, the adjusting screw 15 is turned and threaded into the nut member 14. As the adjusting screw is threaded in, the spring pieces 26 of the washer 18 are compressed by the upper adjusting screw 15 and the lower bottom member 16, which produces frictional resistance to rotation between the adjusting screw 15 and the spring pieces 26 due to the elastic restoring force of the spring pieces 26. The frictional resistance to rotation thus produced prevents rotation of the adjusting screw 15, thus keeping the adjusting screw 15 in threaded engagement in the nut member 14 (initial set position).

Next, as shown in FIG. 1, the lash adjuster 1 is inserted in the receiving hole 13 of the cylinder head 2, and after mounting the arm 6 and the camshaft 12, the camshaft 12 is rotated by cranking. As the camshaft 12 is rotated and every time the cam lobe 10 b of the cam 10 passes the roller 11, an impact load is applied to the adjusting screw 15 that tends to push the adjusting screw 15 into the nut member 14, thus axially vibrating the adjusting screw 15 within the range of the backlash between the external thread 19 and the internal thread 20. This axial vibration causes the adjusting screw 15 to gradually rotate in the direction to protrude from the nut member 14. Thus, the adjusting screw 15 separates from the washer 18 and the initial set position is released. Thereafter, the adjusting screw 15 moves in the direction to protrude from the nut member while rotating, under the biasing force of the return spring 17, thus pushing up the end of the arm 6 until, as shown in FIG. 6, the roller 11 contacts the base circle 10 a of the cam 10.

In this state, when the camshaft 12 is rotated by the engine, and the arm 6 is pushed down by the cam lobe 10 b of the cam 10, the valve 4 separates from the valve seat 9, thus opening the intake port 3. In this state, under the load applied to the adjusting screw 15 that tends to push in the adjusting screw 15, the pressure flank 21 of the external thread 19 is received by the pressure flank 21 of the internal thread 20, so that the axial position of the adjusting screw 15 is fixed.

When the cam 10 further rotates and the cam lobe 10 b separates from the roller 11, the valve stem 5 rises under the biasing force of the valve spring 8 until the valve 4 is seated on the valve seat 9, closing the intake port 9.

Strictly speaking, when the arm 6 is pushed down by the cam lobe 10 b of the cam 10, the adjusting screw 15 is pushed in due to a slight slip between the pressure flanks 21 of the external and internal threads 19 and 20. But once the cam lobe 10 b separates from the roller 11 and the load that tends to push in the adjusting screw 15 is removed, the adjusting screw 15 protrudes and returns to the original position under the load in the protruding direction applied from the return spring 17.

If the distance between the cam 10 and the arm 6 increases while the engine is running due to differences in thermal expansion coefficient among the component parts of the valve gear, including the cylinder head 2, valve stem 5 and arm 6, the adjusting screw 15 protrudes by a longer distance when the cam 10 rotates from the position where the arm 6 is pushed down by the cam lobe 10 b until the load tending to push in the adjusting screw is released than the distance by which the adjusting screw 15 is pushed in when the arm 6 is pushed down by the cam lobe 10 b of the cam 10. Thus in this state, with the rotation of the cam 10, the adjusting screw 15 gradually protrudes, thereby eliminating any gap between the base circle 10 a of the cam 10 and the roller 11.

Conversely, if the contact surfaces of the valve 4 and the valve seat 9 become worn, since the biasing force of the valve spring 8 acts on the adjusting screw 15 even while the base circle 10 a of the cam 10 is facing the roller 11, the adjusting screw 15 protrudes by a shorter distance when the cam 10 rotates from the position where the arm 6 is pushed down by the cam lobe 10 b until the load tending to push in the adjusting screw is released than the distance by which the adjusting screw 15 is pushed in when the arm 6 is pushed down by the cam lobe 10 b of the cam 10. Thus in this state, with the rotation of the cam 10, the adjusting screw 15 gradually pushed in, thereby eliminating any gap between the contact surfaces of the valve 4 and the valve seat 9.

When the camshaft 12 is dismounted from the valve for the overhaul of the engine, the adjusting screw 15 protrudes from the nut member 14 under the biasing force of the return spring 17. Thus, when reassembling the camshaft on the valve gear, the adjusting screw 15 has to be threaded into the nut member 14 to the initial set position before mounting the camshaft 12.

With this lash adjuster 1, since the adjusting screw 15 is moved into the initial set position using the frictional resistance to rotation produced when the adjusting screw 15 is threaded into the nut member 14, the adjusting screw 15 can be repeatedly moved into the initial set position.

With this lash adjuster 1, since the adjusting screw 15 can be moved into the initial set position simply by driving the adjusting screw 15 into the nut member 14, initial setting can be carried out more easily than with a lash adjuster in which an initial setting member has to be mounted after driving the adjusting screw 15.

With this lash adjuster 1, when the camshaft 12 is rotated with the lash adjuster mounted to the valve gear, the initial set position is automatically released by the impact load applied to the adjusting screw 15. Thus, an operator does not have to remember to release the initial set position of the adjusting screw 15 when the lash adjuster 1 is mounted in the valve gear.

With this lash adjuster 1, since the washer 18 is retained between the adjusting screw 15 and the bottom member 16 after the initial set position of the adjusting screw 15 has been released, no separate member such as a set pin is necessary when the initial set position of the adjusting screw 15 is released. Thus, there is no possibility of inadvertently leaving such a separate member in the engine when the initial set position of the adjusting screw is released. Also, there is no need to keep a separate member such as a set pin in stock after the lash adjuster 1 has been mounted in the valve gear in preparation for overhaul.

The lash adjuster 1 is inexpensive because there is no need to form holes for inserting the set pin in the adjusting screw 15 and the nut member 14.

With this lash adjuster 1, since the elastic restoring force produced by the spring pieces 26 of the washer 18 when the adjusting screw 15 is threaded into the nut member 14 is symmetrical with respect to the axis of the washer 18, the adjusting screw 15 is less likely to incline in the initial set position.

Since the washer 18 is an annular member which can surround the return spring 17, this washer 18 can be mounted in a conventional lash adjuster to constitute the lash adjuster 1 according to the present invention. Such a lash adjuster can be manufactured at a low cost.

With this lash adjuster 1, since the spring pieces 26 extend in a direction to bias the adjusting screw 15 in the loosening direction, when an impact load is applied to the adjusting screw 15 while the adjusting screw is in the initial set position, the adjusting screw 15 easily rotates in the direction to protrude from the nut member 14. Thus, it is possible to reliably release the initial set position of the adjusting screw 15 by cranking the engine.

In this embodiment, as the initial setting means, the washer 18 is used, which include the circumferentially extending spring pieces 26 formed by cutting and raising an annular sheet. This type of washer 18 can be axially compressed by a larger amount than other types washers (such as a toothed washer having teeth radially extending from an annular sheet), so that it is possible to more reliably prevent inadvertent release of the initial set position of the adjusting screw 15 even if unintended vibrations or impacts are applied to the adjusting screw 15, thereby ensuring safe transport of the lash adjuster 1. But instead of this washer 18, an externally toothed washer 28 as shown in FIGS. 7( a) and 7(b) may be used, which includes teeth 27 extending radially outwardly from an annular sheet (such as the one stipulated under JIS B1251 (revised in 2001)).

In this case, the teeth 27 of the toothed washer 28 are preferably twisted so as to bias the adjusting screw 15 in the loosening direction (twisted such that each tooth 27 becomes closer to the adjusting screw 15 in the counterclockwise direction, as viewed from the adjusting screw 15, if the external thread 19 has a right-hand twist). This toothed washer 28 can be formed by pressing a spring steel material.

Also, instead of the washer 18, still another type of toothed washer may be used (such as an internally toothed washer, toothed conical washer or a both internally and externally toothed washer, as stipulated under JIS B1251)).

Further, the washer 18 may be replaced by a conical spring washer formed by bending an annular sheet in a tapered shape (such as a conical spring washer as stipulated under JIS B1251), a corrugated spring washer formed by corrugating an annular sheet (such as a corrugated spring washer stipulated under JIS B1251), or a spring washer formed by helically winding a wire member by one round (such as a spring washer stipulated under JIS B1251).

The bottom member 16 may be fixed to the bottom end of the nut member 14 by pressing or by welding to the bottom end of the nut member 14. Alternatively, the nut member 14 and the bottom member 16 may be formed integral with each other.

FIG. 8 shows a valve gear in which the lash adjuster 31 of the second embodiment is mounted. As with the first embodiment, this valve gear includes a valve 34 provided at an intake port 33 of a cylinder head 32, and a valve stem 35 connected to the valve 34. The valve stem 35 extends upwardly from the valve 34. A spring retainer 36 is fixed to the upper portion of the valve stem 35. A valve spring 37 biases the spring retainer 36 upwardly, thereby seating the valve 34 on a valve seat 38.

As shown in FIGS. 8 to 10, the lash adjuster 31 includes a lifter body 40 vertically slidably inserted in a guide hole 39 formed in the cylinder head 32, a nut member 41 vertically slidable together with the lifter body 40, an adjusting screw 44 having an external thread formed on its outer periphery and in threaded engagement with an internal thread formed on the inner periphery of the nut member 41, and a return spring 45 biasing the adjusting screw 44. The lifter body 40 comprises a cylindrical portion 46, and an end plate 47 provided at the top end of the cylindrical portion 46. The nut member 41 is fixed to the bottom surface of the end plate 47 by means of a snap ring 48, with the top end of the nut member 41 closed by the end plate 47.

As shown in FIG. 8, a cam 49 is provided over the lifter body 40. The cam 49 is integrally formed on a camshaft 50 which rotates in unison with an engine crankshaft (not shown) so that when the camshaft 50 rotates, a cam lobe 49 b which bulges from a base circle 49 a presses the top surface of the end plate 47, thereby pushing down the lifter body 40.

As shown in FIGS. 9 and 10, the return spring 45 is mounted between the adjusting screw 44 and the end plate 47, thereby biasing the adjusting screw 44 in the direction to protrude downwardly from the nut member 41. Thus, the adjusting screw 44 presses the top end of the valve stem 35 at its end protruding from the nut member 41 (see FIG. 8).

The external thread 43 and the internal thread 42 both have a pressure flank 51 for receiving pressure when a load is applied to the adjusting screw 44 that tends to push the adjusting screw 44 into the nut member 41, and a clearance flank 52, with the pressure flank having a larger flank angle than the clearance flank, so that the threads 42 and 43 have a serration-shaped longitudinal section. With this arrangement, when a static load is applied to the adjusting screw 44 that tends to push in the adjusting screw, the rotation of the adjusting screw 44 is prevented due to the frictional resistance between the pressure flanks 51 of the external thread 43 and the internal thread 42. On the other hand, when a static load is applied to the adjusting screw 44 that tends to push out the adjusting screw, slip occurs between the clearance flanks 52 of the external thread 43 and the internal thread 42, thus allowing rotation of the adjusting screw 44.

An annular toothed washer 53 is provided between the adjusting screw 44 and the end plate 47 so as to surround the return spring 45 and to face the end of the adjusting screw 44 inserted in the nut member 41. As shown in FIGS. 11( a) and 11(b), the toothed washer 53 has a plurality of teeth 54 radially extending from an annular sheet and adapted to be sandwiched between the adjusting screw 44 and the end plate 47 when the adjusting screw 44 is threaded into the nut member 41 (see FIGS. 9 and 10). The teeth 54 are twisted so as to bias the adjusting screw 44 in the loosening direction (twisted such that each tooth 54 becomes closer to the adjusting screw 44 in the counterclockwise direction, as viewed from the adjusting screw 44, if the external thread 43 has a right-hand twist).

With this lash adjuster 31, with the adjusting screw 44 protruding from the nut member 41 as shown in FIG. 9, when the adjusting screw 44 is turned and threaded into the nut member 41, the teeth 54 of the toothed washer 53 are compressed by the upper end plate 47 and the lower adjusting screw 44 as shown in FIG. 10, which produces frictional resistance to rotation between the adjusting screw 44 and the teeth 54 due to the elastic restoring force of the teeth 54. The frictional resistance to rotation thus produced prevents rotation of the adjusting screw 44, thus keeping the adjusting screw 44 in the initial set position.

Then, with the lash adjuster 31 mounted in the valve gear as shown in FIG. 8, when the camshaft 50 is rotated by cranking the engine, every time the cam lobe 49 b of the cam 49 passes the end plate 47, an impact load is applied to the adjusting screw 44, thus releasing the initial set position. As a result, the adjusting screw 44 protrudes while rotating under the biasing force of the return spring 45, thereby raising the lifter body 40 until the end plate 47 contacts the base circle 49 a of the cam 49.

With this lash adjuster 31, as with the first embodiment, since the adjusting screw 44 is moved into the initial set position utilizing the frictional resistance to rotation produced when the adjusting screw 44 is threaded into the nut member 41, the adjusting screw 44 can be repeatedly moved into the initial set position.

With this lash adjuster 31, the adjusting screw 44 can be moved into the initial set position simply by driving the adjusting screw 44 into the nut member 41. Thus, initial setting can be carried out more easily than with a lash adjuster in which an initial setting member has to be mounted after driving the adjusting screw 44.

With this lash adjuster 31, when the camshaft 50 is rotated with the lash adjuster mounted to the valve gear, the initial set position is automatically released by the impact load applied to the adjusting screw 44. Thus, an operator does not have to remember to release the initial set position of the adjusting screw 44 when the lash adjuster 31 is mounted in the valve gear.

With this lash adjuster 31, since the toothed washer 53 is retained between the adjusting screw 44 and the end plate 47 after the initial set position of the adjusting screw 44 has been released, no separate member such as a set pin is necessary when the initial set position of the adjusting screw 44 is released. Thus, there is no possibility of inadvertently leaving such a separate member in the engine when the initial set position of the adjusting screw is released. Also, there is no need to keep a separate member such as a set pin in stock after the lash adjuster 31 has been mounted in the valve gear in preparation for overhaul.

The lash adjuster 31 is inexpensive because there is no need to form holes for inserting the set pin in the adjusting screw 44 and the nut member 41.

Since the toothed washer 53 is an annular member which can surround the return spring 45, this washer 53 can be mounted in a conventional lash adjuster to constitute the lash adjuster 31 according to the present invention. Such a lash adjuster can be manufactured at a low cost.

With this lash adjuster 31, since the teeth 54 are twisted so as to bias the adjusting screw 44 in the loosening direction, when an impact load is applied to the adjusting screw 44 while the adjusting screw is in the initial set position, the adjusting screw 44 easily rotates in the direction to protrude from the nut member 41. Thus, it is possible to reliably release the initial set position of the adjusting screw 44 by cranking the engine.

In this embodiment, as the initial setting means, the toothed washer 53 is used, which include the teeth 54 radially extending from the annular sheet. But instead of this toothed washer 53, the washer 18 used in the first embodiment may be used (see FIG. 5), which includes the circumferentially extending spring pieces 26 formed by cutting and raising portions of an annular sheet, or any other type of washer may be used (such as a corrugated spring washer, a conical spring washer, or a spring washer).

FIG. 12 shows a valve gear in which the lash adjuster 61 of the third embodiment is mounted. This valve gear includes a valve 64 provided at an intake port 63 of a cylinder head 62 of an engine, a valve stem 65 connected to the valve 64, and an arm 67 pivotable about a pivot shaft 66.

The valve stem 65 extends upwardly from the valve 64. A spring retainer 68 is fixed to the upper portion of the valve stem 65. A valve spring 69 biases the spring retainer 68 upwardly, thereby seating the valve 64 on a valve seat 70.

The arm 67 has its mid-portion pivotally supported on the pivot shaft 66. A roller 71 is mounted on one end of the arm 67, and the lash adjuster 61 is mounted in the other end of the arm 67. A cam 72 provided under the arm 67 is integrally formed on a camshaft 73 which rotates in unison with an engine crankshaft (not shown) so that when the camshaft 73 rotates, a cam lobe 72 b which bulges from a base circle 72 a pushes the roller 71, thereby pivoting the arm 67.

As shown in FIGS. 13 and 14, the lash adjuster 61 includes a nut member 74, an adjusting screw 75, and a return spring 76. The nut member 74 is received in a hole 77 extending vertically through the arm 67 and has an internal thread 78 on its inner periphery which is in threaded engagement with an external thread 79 formed on the outer periphery of the adjusting screw 75.

The nut member 74 has its top end protruding from the top surface of the arm 67. A cap 80 is fitted on the protruding end of the nut member, thereby closing the top end of the nut member 74. The cap 80 engages the top edge of the hole 77, preventing the nut member 74 from downwardly separating from the hole 77. The nut member 74 has a flange 81 at its bottom end which abuts the bottom surface of the arm 67, thereby receiving upward force applied to the nut member 74.

The external thread 79 and the internal thread 78 both have a pressure flank 82 for receiving pressure when a load is applied to the adjusting screw 75 that tends to push the adjusting screw 75 into the nut member 74, and a clearance flank 83, with the pressure flank having a larger flank angle than the clearance flank, so that the threads 78 and 79 have a serration-shaped longitudinal section. With this arrangement, when a static load is applied to the adjusting screw 75 that tends to push in the adjusting screw, the rotation of the adjusting screw 75 is prevented due to the frictional resistance between the pressure flanks 82 of the external thread 79 and the internal thread 78. On the other hand, when a static load is applied to the adjusting screw 75 that tends to push out the adjusting screw, slip occurs between the clearance flanks 83 of the external thread 79 and the internal thread 78, thus allowing rotation of the adjusting screw 75.

The return spring 76 is mounted between the cap 80 and the adjusting screw 75, biasing the adjusting screw 75 in the direction to protrude downwardly from the nut member 74. Thus, the adjusting screw 75 presses the top end of the valve stem 65 at its protruding end (see FIG. 12).

An annular toothed washer 84 is provided between the adjusting screw 75 and the cap 80 so as to surround the return spring 76 and to face the end of the adjusting screw 75 inserted in the nut member 74. The toothed washer 84 has a plurality of teeth 85 radially extending from an annular sheet and adapted to be sandwiched between the adjusting screw 75 and the cap 80 when the adjusting screw 75 is threaded into the nut member 74. The teeth 85 are twisted so as to bias the adjusting screw 75 in the loosening direction (twisted such that each tooth 85 becomes closer to the adjusting screw 75 in the counterclockwise direction, as viewed from the adjusting screw 75, if the external thread 79 has a right-hand twist).

With this lash adjuster 61, with the adjusting screw 75 protruding from the nut member 74 as shown in FIG. 13, when the adjusting screw 75 is turned and threaded into the nut member 74, the teeth 85 of the toothed washer 84 are compressed by the upper cap 80 and the lower adjusting screw 75 as shown in FIG. 14, which produces frictional resistance to rotation between the adjusting screw 75 and the teeth 85 due to the elastic restoring force of the teeth 85. The frictional resistance to rotation thus produced prevents rotation of the adjusting screw 75, thus keeping the adjusting screw 75 in the initial set position.

Then, with the lash adjuster 61 mounted in the valve gear as shown in FIG. 12, when the camshaft 73 is rotated by cranking the engine, every time the cam lobe 72 b of the cam 72 passes the roller 71, an impact load is applied to the adjusting screw 75, thus releasing the initial set position of the adjusting screw 75. As a result, the adjusting screw 75 protrudes while rotating under the biasing force of the return spring 76, thereby pivoting the arm 67 until the roller 71 contacts the base circle 72 a of the cam 72.

With this lash adjuster 61, as with the first embodiment, since the adjusting screw 75 is moved into the initial set position utilizing the frictional resistance to rotation produced when the adjusting screw 75 is threaded into the nut member 74, the adjusting screw 75 can be repeatedly moved into the initial set position.

With this lash adjuster 61, the adjusting screw 75 can be moved into the initial set position simply by driving the adjusting screw 75 into the nut member 74. Thus, initial setting can be carried out more easily than with a lash adjuster in which an initial setting member has to be mounted after driving the adjusting screw 75.

With this lash adjuster 61, when the camshaft 73 is rotated with the lash adjuster mounted to the valve gear, the initial set position is automatically released by the impact load applied to the adjusting screw 75. Thus, an operator does not have to remember to release the initial set position of the adjusting screw 75 when the lash adjuster 61 is mounted in the valve gear.

With this lash adjuster 61, since the toothed washer 84 is retained between the adjusting screw 75 and the cap 80 after the initial set position of the adjusting screw 75 has been released, no separate member such as a set pin is necessary when the initial set position of the adjusting screw 75 is released. Thus, there is no possibility of inadvertently leaving such a separate member in the engine when the initial set position of the adjusting screw is released. Also, there is no need to keep a separate member such as a set pin in stock after the lash adjuster 61 has been mounted in the valve gear in preparation for overhaul.

The lash adjuster 61 is inexpensive because there is no need to form holes for inserting the set pin in the adjusting screw 75 and the nut member 74.

With this lash adjuster 61, since the toothed washer 84 is an annular member which can surround the return spring 76, this washer 84 can be mounted in a conventional lash adjuster to constitute the lash adjuster 61 according to the present invention. Such a lash adjuster 61 can be manufactured at a low cost.

With this lash adjuster 61, since the teeth 85 are twisted so as to bias the adjusting screw 75 in the loosening direction, when an impact load is applied to the adjusting screw 75 while the adjusting screw is in the initial set position, the adjusting screw 75 easily rotates in the direction to protrude from the nut member 74. Thus, it is possible to reliably release the initial set position of the adjusting screw 75 by cranking the engine.

In this embodiment, as the initial setting means, the toothed washer 84 is used, which include the teeth 85 radially extending from the annular sheet. But instead of this toothed washer 84, the washer used in the first embodiment may be used, which includes the circumferentially extending spring pieces formed by cutting and raising portions of an annular sheet, or any other type of washer may be used (such as a corrugated spring washer, a conical spring washer, or a spring washer).

FIG. 15 shows a lash adjuster 90 of the fourth embodiment according to the present invention. Elements corresponding to those of the first embodiment are denoted by identical numerals and their description is omitted.

The adjusting screw 15 of this embodiment has a head 91 protruding from the nut member 14 and having an outer diameter larger than the inner diameter of the nut member 14. As shown in FIG. 16, the head 91 is engaged in a recess 25 formed in the bottom surface of the arm 6, pivotally supporting the arm 6.

A tapered surface 92 having a downwardly decreasing diameter is formed on the outer periphery of the head 91 at its bottom end. When the adjusting screw 15 is threaded into the nut member 14, the tapered surface 92 of the head 91 is adapted to contact a tapered surface 93 formed on the inner periphery of the nut member 14 at its top end.

With this lash adjuster 90, when the adjusting screw 15 is rotated and threaded into the nut member 14 from the state in which the adjusting screw 15 protrudes from the nut member 14 as shown by the chain line in FIG. 15, the tapered surface 92 of the head 91 of the adjusting screw 15 contacts the tapered surface 93 of the nut member 14, as shown by the solid line in FIG. 15. When the adjusting screw 15 is further driven in, the portion of the adjusting screw 15 inserted in the nut member 14 is axially pulled into the nut member. The adjusting screw 15 is thus pulled and deformed. This produces frictional resistance to rotation between the head 91 and the nut member 14 due to the elastic restoring force of the adjusting screw 15. The frictional resistance to rotation thus produced prevents rotation of the adjusting screw 15, thus keeping the adjusting screw in the initial set position.

Preferably, in order to more reliably prevent rotation of the adjusting screw 15, any oil adhered to tapered surfaces 92 and 93 of the adjusting screw 15 and the nut member 14 is removed beforehand by degreasing.

With this lash adjuster 90, when the adjusting screw 15 is threaded into the nut member 14, the tapered surfaces 92 and 93 contact each other. Due to the wedge effect when the tapered surfaces 92 and 93 contact each other, a large frictional force is produced between the tapered surfaces 92 and 93, which makes it possible to reliably prevent rotation of the adjusting screw 15.

Also with this lash adjuster 90, since the elastic restoring force produced by the adjusting screw 15 when the adjusting screw 15 is threaded into the nut member 14 is symmetrical with respect to the axis, the adjusting screw 15 is less likely to incline in the initial set position.

With this lash adjuster 90, when the camshaft 12 is rotated with the lash adjuster mounted to the valve gear, the initial set position of the adjusting screw 15 is automatically released by the impact load applied to the adjusting screw 15. Thus, an operator does not have to remember to release the initial set position of the adjusting screw 15 when the lash adjuster 90 is mounted in the valve gear.

With this lash adjuster 90, when the camshaft is rotated with the lash adjuster mounted to the valve gear, the initial set position is automatically released by the impact load applied to the adjusting screw 15. Thus, an operator does not have to remember to release the state in which the adjusting screw 15 is prevented from being rotated when mounting the lash adjuster 90 in the valve gear.

With this lash adjuster 90, since the adjusting screw 15 is prevented from being rotated without using a separate member such as a set pin, there is no need to keep a separate member such as a set pin in stock after the lash adjuster 90 has been mounted in the valve gear in preparation for overhaul.

FIG. 17 shows a lash adjuster 100 of the fifth embodiment according to the present invention. Elements corresponding to those of the second embodiment are denoted by identical numerals and their description is omitted.

The adjusting screw 44 includes a head 101 protruding from the nut member 41 and having an outer diameter larger than the inner diameter of the nut member 41. As shown in FIG. 18, the head 101 presses the top end of the valve stem 35.

As shown in FIG. 17, a tapered surface 102 having an upwardly decreasing diameter is formed on the outer periphery of the head 101 at its top end. When the adjusting screw 44 is threaded into the nut member 41, the tapered surface 102 of the head 101 is adapted to be brought into contact with a tapered surface 103 formed on the inner periphery of the nut member 41 at its bottom end.

With this lash adjuster 100, when the adjusting screw 44 is rotated and threaded into the nut member 41 from the state in which the adjusting screw 44 protrudes from the nut member 41 as shown by the chain line in FIG. 17, the tapered surface 102 of the head 101 of the adjusting screw 44 contacts the tapered surface 103 of the nut member 41, as shown by the solid line in FIG. 17. When the adjusting screw 44 is further driven in, the portion of the adjusting screw 44 inserted in the nut member 41 is axially pulled into the nut member. The adjusting screw 44 is thus pulled and deformed. This produces frictional resistance to rotation between the head 101 and the nut member 41 due to the elastic restoring force of the adjusting screw 44. The frictional resistance to rotation thus produced prevents rotation of the adjusting screw 44, thus keeping the adjusting screw in the initial set position. Preferably, the adjusting screw 44 and the nut member 41 are degreased beforehand.

Also with this lash adjuster 100, since the elastic restoring force produced by the adjusting screw 44 when the adjusting screw 44 is threaded into the nut member 41 is symmetrical with respect to the axis, the adjusting screw 44 is less likely to incline in the initial set position.

With this lash adjuster 100, when the camshaft 50 is rotated with the lash adjuster mounted to the valve gear, the initial set position of the adjusting screw 44 is automatically released by the impact load applied to the adjusting screw 44. Thus, an operator does not have to remember to release the initial set position of the adjusting screw 44 when the lash adjuster 100 is mounted in the valve gear.

With this lash adjuster 100, when the camshaft 50 is rotated with the lash adjuster mounted to the valve gear, the state in which the adjusting screw 44 is prevented from rotating is released by the impact load applied to the adjusting screw 44. Thus, an operator does not have to remember to release the state in which the adjusting screw 44 is prevented from being rotated when mounting the lash adjuster 100 in the valve gear.

FIG. 19 shows a lash adjuster 110 of the sixth embodiment according to the present invention. Elements corresponding to those of the third embodiment are denoted by the identical numerals and their description is omitted.

The adjusting screw 75 includes a head 111 protruding from the nut member 74 and having an outer diameter larger than the inner diameter of the nut member 74. The head 111 presses the top end of the valve stem 65.

A tapered surface 112 having an upwardly decreasing diameter is formed on the outer periphery of the head 111 at its top end. When the adjusting screw 75 is threaded into the nut member 74, the tapered surface 112 of the head 111 is adapted to be brought into contact with a tapered surface 113 formed on the inner periphery of the nut member 74 at its bottom end.

With this lash adjuster 110, when the adjusting screw 75 is rotated and threaded into the nut member 74 from the state in which the adjusting screw 75 protrudes from the nut member 74 as shown by the chain line in FIG. 19, the tapered surface 112 of the head 111 of the adjusting screw 75 contacts the tapered surface 113 of the nut member 74, as shown by the solid line in FIG. 19. When the adjusting screw 75 is further driven in, the portion of the adjusting screw 75 inserted in the nut member 74 is axially pulled into the nut member. The adjusting screw 75 is thus pulled and deformed. This produces frictional resistance to rotation between the head 111 and the nut member 74 due to the elastic restoring force of the adjusting screw 75. The frictional resistance to rotation thus produced prevents rotation of the adjusting screw 75, thus keeping the adjusting screw in the initial set position. Preferably, the adjusting screw 75 and the nut member 74 are degreased beforehand.

Also with this lash adjuster 110, since the elastic restoring force produced by the adjusting screw 75 when the adjusting screw 75 is threaded into the nut member 74 is symmetrical with respect to the axis, the adjusting screw 75 is less likely to incline in the initial set position.

With this lash adjuster 110, when the camshaft 73 is rotated with the lash adjuster mounted to the valve gear, the initial set position of the adjusting screw 75 is automatically released by the impact load applied to the adjusting screw 75. Thus, an operator does not have to remember to release the initial set position of the adjusting screw 75 when the lash adjuster 110 is mounted in the valve gear.

With this lash adjuster 110, when the camshaft 73 is rotated with the lash adjuster mounted to the valve gear, the state in which the adjusting screw 75 is prevented from rotating is released by the impact load applied to the adjusting screw 75. Thus, an operator does not have to remember to release the state in which the adjusting screw 75 is prevented from being rotated when mounting the lash adjuster 110 in the valve gear.

FIGS. 20 and 21 show a lash adjuster 120 of the seventh embodiment according to the present invention. Elements corresponding to those of the first embodiment are denoted by identical numerals and their description is omitted.

A circumferential groove 121 is formed in the outer periphery of the portion of the adjusting screw 15 protruding from the nut member 14. A rubber O-ring 122 is fitted in the circumferential groove 121. The O-ring 122 has an outer diameter larger than the inner diameter of the nut member 14, and its portion radially outwardly protruding from the circumferential groove 121 is located right over the top end surface of the nut member 14. The O-ring 122 may e.g. be made of fluororubber, silicon rubber or acrylic rubber.

With this lash adjuster 120, when the adjusting screw 15 is rotated and threaded into the nut member 14 from the state in which the adjusting screw 15 protrudes from the nut member 14 as shown in FIG. 21, the O-ring 122 is pressed by the top end surface of nut member 14 and deformed in the axial direction as shown in FIG. 22. This produces frictional resistance to rotation between the O-ring 122 and the top end surface of the nut member 14 due to the elastic restoring force of the O-ring 122. The frictional resistance to rotation thus produced prevents rotation of the adjusting screw 15, thus keeping the adjusting screw 15 in the initial set position.

With this lash adjuster 120, since the O-ring 122 is deformed by a larger amount than a metal when the adjusting screw 15 is threaded into the nut member 14, it is possible to control the frictional resistance to rotation produced between the O-ring 122 and the top end surface of the nut member 14 by adjusting the axial displacement of the adjusting screw 15.

Also with this lash adjuster 120, since the elastic restoring force produced by the O-ring 122 when the adjusting screw 15 is threaded into the nut member 14 is symmetrical with respect to the axis, the adjusting screw 15 is less likely to incline in the initial set position.

With this lash adjuster 120, when the camshaft 12 is rotated with the lash adjuster mounted to the valve gear, the initial set position of the adjusting screw 15 is automatically released by the impact load applied to the adjusting screw 15. Thus, an operator does not have to remember to release the initial set position of the adjusting screw 15 when the lash adjuster 120 is mounted in the valve gear.

With this lash adjuster 120, since the O-ring 122 is retained in the circumferential groove 121 after the initial set position of the adjusting screw 15 has been released, no separate member such as a set pin is necessary when the initial set position of the adjusting screw 15 is released. Thus, there is no possibility of inadvertently leaving such a separate member in the engine when the initial set position of the adjusting screw is released. Also, there is no need to keep a separate member such as a set pin in stock after the lash adjuster 120 has been mounted in the valve gear in preparation for overhaul.

The initial set position can also be released by inserting a tool T between the O-ring 122 and the bottom end surface of the nut member 14 as shown by chain line in FIG. 20, thereby forming a gap between the O-ring 122 and the bottom end surface of the nut member 14.

Since the O-ring 122 fitted in the circumferential groove 121 of this lash adjuster 120 is widely commercially available, it is inexpensive.

With this lash adjuster 120, the O-ring 122 is used as the initial setting means for preventing rotation of the adjusting screw 15. But a ring member made of an elastic resin such as a thermoplastic elastomer may be used instead.

Also as shown in FIG. 24, a conical coil spring 123 may be used as the initial setting means for preventing rotation of the adjusting screw 15. The conical coil spring 123 is fitted in a circumferential groove 121 formed in the outer periphery of the portion of the adjusting screw 15 protruding from the nut member 14. The conical coil spring 123 is a conical member having an upwardly decreasing diameter with its top end engaged in the circumferential groove 121 with a radial interference fit. Its bottom end has an outer diameter larger than the inner diameter of the nut member 14 such that its portion radially outwardly protruding from the circumferential groove 121 is located right over the top end surface of the nut member 14. The conical coil spring 123 may e.g. be made of spring steel.

The conical coil spring 123 is integrally formed with a resetting tab 124 radially outwardly extending from its bottom end.

With this lash adjuster 125, when the adjusting screw 15 is turned and threaded into the nut member 14 from the state in which the adjusting screw 15 protrudes from the nut member 14 as shown in FIG. 24, the conical coil spring 123 is pressed against the top end surface of the nut member 14 and deformed as shown in FIG. 25. This produces frictional resistance to rotation between the bottom end of the conical coil spring 123 and the top end surface of the nut member 14 due to the elastic restoring force of the conical coil spring 123. The frictional resistance to rotation thus produced prevents rotation of the adjusting screw 15, thus keeping the adjusting screw 15 in the initial set position.

In this state, by raising the resetting tab 124, thereby forming a gap between the bottom end of the conical coil spring 123 and the top end surface of the nut member 14, the initial set position of the adjusting screw 15 is released, so that the adjusting screw 15 protrudes while rotating under the biasing force of the return spring 17.

By circumferentially moving the resetting tab 124, thereby causing the conical coil spring 123 and the nut member 14 to slip relative to each other, too, since the friction coefficient between the conical coil spring 123 and the nut member 14 changes from a static friction coefficient to a dynamic friction coefficient (which is smaller than a static friction coefficient), it is possible to release the initial set position of the adjusting screw 15. Further, the initial set position can also be released by rotating the camshaft 12 by cranking.

With this lash adjuster 125, since the conical coil spring 123 has its top end engaged in the circumferential groove 121 with a radial interference fit, there will be no backlash between the conical coil spring 123 and the adjusting screw 15, which stabilizes the position of the conical coil spring 123. This in turn stabilizes the contact state of the conical coil spring 123 relative to the top end surface of the nut member 14, thereby making it possible to accurately control the frictional resistance to rotation produced between the conical coil spring 123 and the top end surface of the nut member 14 when bringing the adjusting screw 15 to the initial set position, by adjusting the axial displacement of the adjusting screw 15.

As shown in FIGS. 26 and 27, a cylindrical coil spring 126 may be used as the initial setting means. The cylindrical coil spring 126 comprises two coil windings with each coil winding engaged in the circumferential groove 121 with a radial inference fit. The cylindrical coil spring 126 has an outer diameter larger than the inner diameter of the nut member 14 such that its portion protruding radially outwardly from the circumferential groove 121 located right over the top end surface of the nut member 14. The cylindrical coil spring 126 may be made of e.g. spring steel. The cylindrical coil spring 126 is integrally formed with a resetting tab 127 radially outwardly extending from one end thereof.

With this lash adjuster, when the adjusting screw 15 is turned and threaded into the nut member 14 from the state in which the adjusting screw 15 protrudes from the nut member 14 as shown in FIG. 26, the cylindrical coil spring 126 is pressed against the top end surface of the nut member 14 and deformed axially as shown in FIG. 28. This produces frictional resistance to rotation between the bottom end of the cylindrical coil spring 126 and the top end surface of the nut member 14 due to the elastic restoring force of the cylindrical coil spring 126. The frictional resistance to rotation thus produced prevents rotation of the adjusting screw 15, thus keeping the adjusting screw 15 in the initial set position.

As shown in FIG. 29, a set clip 128 may be used as the initial setting means. The set clip 128 is engaged in a circumferential groove 121 formed in the outer periphery of the portion of the adjusting screw 15 protruding from the nut member 14. The set clip 128 is formed by bending a metal wire and comprises, as shown in FIG. 30, a C-shaped annular portion 129 engaged in the circumferential groove 121 with a radial interference fit, and a pair of resetting tabs 130 radially outwardly extending from the respective ends of the C-shaped annular portion 129.

With this lash adjuster 131, when the adjusting screw 15 is turned and threaded into the nut member 14 from the state in which the adjusting screw 15 protrudes from the nut member 14, the C-shaped annular portion 129 is pressed against the top end surface of the nut member 14 and deformed axially as shown in FIG. 31. This produces frictional resistance to rotation between the C-shaped annular portion 129 and the nut member 14 due to the elastic restoring force of the C-shaped annular portion 129. The frictional resistance to rotation thus produced prevents rotation of the adjusting screw 15, thus keeping the adjusting screw 15 in the initial set position.

As shown in FIG. 29, the C-shaped annular portion 129 may be flat but is more preferably axially corrugated as shown in FIGS. 32 and 33. With this arrangement, when the adjusting screw 15 is threaded into the nut member 14 from the state in which the adjusting screw 15 protrudes from the nut member 14, the C-shaped annular portion 129 is deformed more markedly as shown in FIG. 34, which makes it possible to control the frictional resistance to rotation produced between the C-shaped annular portion 129 and the top end surface of the nut member 14 by adjusting the axial displacement of the adjusting screw 15.

In this state, when the C-shaped annular portion 129 is radially expanded by operating the resetting tabs 130, thereby causing the C-shaped annular portion 129 and the nut member 14 to slip relative to each other, since the friction coefficient between the C-shaped annular portion 129 and the nut member 14 changes from a static friction coefficient to a dynamic friction coefficient (which is smaller than a static friction coefficient), the initial set position of the adjusting screw 15 is released. The initial set position can also be released by rotating the camshaft 12 by cranking.

With this lash adjuster 131, the resetting tabs 130 extend parallel to each other from the respective ends of the C-shaped annular portion 129 so that the C-shaped annular portion 129 can be radially expanded by operating the resetting tabs 130 so as to increase the distance therebetween. But as shown in FIGS. 35 and 36, the resetting tabs 130 may be provided such that the tab extending from one end of the C-shaped annular portion 129 crosses the tab extending from the other end of the C-shaped annular portion 129. With this arrangement, by pressing the pair of resetting tabs 130 from outside to narrow the distance therebetween, the C-shaped annular portion 129 can be radially expanded, so that the initial set position of the adjusting screw 15 can be more easily released.

As shown in FIGS. 37 and 38, a cocoon-shaped clip 132 may be used as the initial setting means. This clip is fitted in a circumferential groove 121 formed in the outer periphery of the portion of the adjusting screw 15 protruding from the nut member 14. The cocoon-shaped clip 132 is formed by bending a metal wire and comprises two C-shaped annular portions 133 and 134 having different centers and coupled together. Of the two C-shaped annular portions 133 and 134, the C-shaped annular portion 133 is axially corrugated. The cocoon-shaped clip 132 is slidable between the position where the C-shaped annular portion 133 is engaged in the circumferential groove 121 and the position where the other C-shaped annular portion 134 is engaged in the circumferential groove 121.

With this lash adjuster 135, with the corrugated C-shaped annular portion 133 engaged in the circumferential groove 121, when the adjusting screw 15 is threaded into the nut member 14, the corrugated C-shaped annular portion 133 is pressed by the nut member 14 and deformed, which produces frictional resistance to rotation between the C-shaped annular portion 133 and the nut member 14 due to the elastic restoring force of the C-shaped annular portion 133. The frictional resistance to rotation thus produced keeps the adjusting screw 15 in the initial set position.

In this state, the initial set position of the adjusting screw 15 can be released by pushing the cocoon-shaped clip 132 in the direction of the arrow of FIG. 38, thereby sliding the clip from the position where the C-shaped annular portion 133 is engaged in the circumferential groove 121 to the position where the other C-shaped annular portion 134 is engaged in the circumferential groove 121. The initial set position can be released by rotating the camshaft 12 by cranking, too.

The C-shaped annular portion 134 may be arcuate as shown in FIG. 38 but may be polygonal too, as shown in FIGS. 40 and 41. Similarly, the C-shaped annular portion 133 may be polygonal. It is important however that, in either case, the annular portions 133 and 134 be engageable in the circumferential groove 121.

FIG. 42 shows a lash adjuster 140 of the eighth embodiment according to this invention. Elements corresponding to those of the second embodiment are denoted by identical numerals and their description is omitted.

A circumferential groove 141 is formed in the outer periphery of the portion of the adjusting screw 44 protruding from the nut member 41. In the circumferential groove 141, a rubber O-ring 142 is fitted. The O-ring 142 has an outer diameter larger than the inner diameter of the nut member 41 such that its portion radially outwardly protruding from the circumferential groove 141 is located right under the bottom end surface of the nut member 41.

With this lash adjuster 140, when the adjusting screw 44 is turned and threaded into the nut member 41 from the state in which the adjusting screw 44 protrudes from the nut member 41 as shown in FIG. 42, the 0-ring 142 is pressed by the bottom end surface of the nut member 41 and deformed in the axial direction as shown in FIG. 43. This produces frictional resistance to rotation between the O-ring 142 and the bottom end surface of the nut member 41 due to the elastic restoring force of the O-ring 142. The frictional resistance to rotation thus produced prevents rotation of the adjusting screw 44, thus keeping the adjusting screw 44 in the initial set position.

Also with this lash adjuster 140, since the elastic restoring force produced by the O-ring 142 when the adjusting screw 44 is threaded into the nut member 41 is symmetrical with respect to the axis, the adjusting screw 44 is less likely to incline in the initial set position.

With this lash adjuster 140, when the camshaft 50 is rotated with the lash adjuster mounted to the valve gear, the initial set position of the adjusting screw 44 is automatically released by the impact load applied to the adjusting screw 44. Thus, an operator does not have to remember to release the initial set position of the adjusting screw 44 when the lash adjuster 140 is mounted in the valve gear.

With this lash adjuster 140, since the O-ring 142 is retained in the circumferential groove 141 after the initial set position of the adjusting screw 44 has been released, no separate member such as a set pin is necessary when the initial set position of the adjusting screw 44 is released. Thus, there is no possibility of inadvertently leaving such a separate member in the engine when the initial set position of the adjusting screw is released. Also, there is no need to keep a separate member such as a set pin in stock after the lash adjuster 140 has been mounted in the valve gear in preparation for overhaul.

With this lash adjuster 140, the O-ring 142 is used as the initial setting means for preventing rotation of the adjusting screw 44. But instead of the O-ring 142, a ring member made of an elastic resin such as a thermoplastic elastomer, as described above, may be used instead. Or a conical coil spring 143 shown in FIGS. 44 and 45 or a cylindrical coil spring 144 shown in FIGS. 46 and 47 may be used instead, too.

FIG. 48 shows a lash adjuster 150 of the ninth embodiment according to the present invention. Elements corresponding to those of the third embodiment are denoted by identical numerals and their description is omitted.

A circumferential groove 151 is formed in the outer periphery of the portion of the adjusting screw 75 protruding from the nut member 74. In the circumferential groove 151, a rubber O-ring 152 is fitted. The O-ring 152 has an outer diameter larger than the inner diameter of the nut member 74 such that its portion radially outwardly protruding from the circumferential groove 151 is located right under the bottom end surface of the nut member 74.

With this lash adjuster 150, when the adjusting screw 75 is turned and threaded into the nut member 74, the O-ring 152 is pressed by the bottom end surface of the nut member 74 and deformed in the axial direction as shown in FIG. 48. This produces frictional resistance to rotation between the O-ring 152 and the bottom end surface of the nut member 74 due to the elastic restoring force of the O-ring 152. The frictional resistance to rotation thus produced prevents rotation of the adjusting screw 75, thus keeping the adjusting screw 75 in the initial set position.

Also with this lash adjuster 150, since the elastic restoring force produced by the O-ring 142 when the adjusting screw 75 is threaded into the nut member 74 is symmetrical with respect to the axis, the adjusting screw 75 is less likely to incline in the initial set position.

With this lash adjuster 150, when the camshaft 73 is rotated with the lash adjuster mounted to the valve gear, the initial set position of the adjusting screw 75 is automatically released by the impact load applied to the adjusting screw 75. Thus, an operator does not have to remember to release the initial set position of the adjusting screw 75 when the lash adjuster 150 is mounted in the valve gear.

With this lash adjuster 150, since the O-ring 152 is retained in the circumferential groove 151 after the initial set position of the adjusting screw 75 has been released, no separate member such as a set pin is necessary when the initial set position of the adjusting screw 44 is released. Thus, there is no possibility of inadvertently leaving such a separate member in the engine when the initial set position of the adjusting screw is released. Also, there is no need to keep a separate member such as a set pin in stock after the lash adjuster 150 has been mounted in the valve gear in preparation for overhaul.

Instead of the O-ring 152, a ring member made of an elastic resin such as a thermoplastic elastomer, as described above, may be used instead. Or a conical coil spring, a cylindrical coil spring, a set clip or a cocoon-shaped clip, as described above, may be used instead, too. 

1. A lash adjuster comprising: a nut member (14) having an internal thread (20) on an inner periphery thereof: an adjusting screw (15) having an external thread (19) formed on an outer periphery thereof and in threaded engagement with the internal thread (20); a return spring (17) biasing the adjusting screw (15) in a direction to protrude from the nut member (14); and an initial setting means (18) configured to be deformed in an axial direction when the adjusting screw (15) is threaded into the nut member (14), thereby producing frictional resistance to rotation that tends to prevent rotation of the adjusting screw (15) due to an elastic restoring force of the initial setting means (18).
 2. The lash adjuster of claim 1 wherein said initial setting means (18) produces said elastic restoring force so as to be symmetrical with respect to the axis.
 3. The lash adjuster of claim 1 wherein said initial setting means (18) is an elastic member located so as to oppose an end of the adjusting screw (15) that is inserted in the nut member (14).
 4. The lash adjuster of claim 3 wherein said elastic member is a washer (18) comprising an annular sheet having circumferentially extending spring pieces (26) formed by cutting and raising portions of the annular sheet.
 5. The lash adjuster of claim 4 wherein said spring pieces (26) are cut and raised in a direction to bias the adjusting screw (15) in a loosening direction.
 6. The lash adjuster of claim 5 wherein said washer (18) is formed by pressing spring steel.
 7. The lash adjuster of claim 3 wherein said elastic member is a toothed washer (28) comprising an annular sheet and teeth radially extending from the annular sheet.
 8. The lash adjuster of claim 7 wherein the teeth (27) of the toothed washer (28) are twisted in a direction to bias the adjusting screw (15) in a loosening direction.
 9. The lash adjuster of claim 8 wherein said toothed washer (28) is formed by pressing spring steel.
 10. The lash adjuster of claim 3 wherein said elastic member is a conical spring washer.
 11. The lash adjuster of claim 3 wherein said elastic member is a corrugated spring washer.
 12. The lash adjuster of claim 3 wherein said elastic member is a spring washer.
 13. The lash adjuster of claim 2 wherein said adjusting screw includes a head (91) protruding from the nut member (14) and having an outer diameter larger than the inner diameter of the nut member (14), whereby said adjusting screw serves as said initial setting means (15).
 14. The lash adjuster of claim 13 wherein said adjusting screw (15) has a tapered surface (92) formed on its portion protruding from the nut member (14), said tapered surface (92) being configured to be brought into contact with a tapered surface (93) formed on the nut member (14) when the adjusting screw (15) is threaded into the nut member (14), thereby producing frictional resistance to rotation.
 15. The lash adjuster of claim 14 wherein said adjusting screw (15) and the nut member (14) are degreased.
 16. The lash adjuster of claim 2 wherein said initial setting means (122) is an annular member engaged in a circumferential groove (121) formed in an outer periphery of a portion of the adjusting screw (15) protruding from the nut member (14) and having an outer diameter larger than the inner diameter of the nut member (14).
 17. The lash adjuster of claim 16 wherein said annular member is an O-ring (122) made of rubber.
 18. The lash adjuster of claim 16 wherein said annular member is a ring made of an elastic resin.
 19. The lash adjuster of claim 16 wherein said annular member is a conical coil spring (123) having a small-diameter end engaged in the circumferential groove (121) with a radial interference fit.
 20. The lash adjuster of claim 16 wherein said annular member is a cylindrical coil spring (126) comprising two coil windings and engaged in the circumferential groove (121) with a radial interference fit.
 21. The lash adjuster of claim 16 wherein said annular member is a cocoon-shaped clip (132) comprising two C-shaped annular portions (133 and 134) having different centers and coupled together, one of said two C-shaped annular portions (133) being corrugated in the axial direction, and wherein said cocoon-shaped clip (132) is slidable between a position where said one C-shaped annular portion (133) is engaged in the circumferential groove (121) and a position where the other C-shaped annular portion (134) is engaged in the circumferential groove (121).
 22. The lash adjuster of claim 21 wherein said C-shaped annular portions (133 and 134) are circular or polygonal.
 23. The lash adjuster of claim 16 wherein said annular member is a set clip (128) comprising a C-shaped annular portion (129) engaged in the circumferential groove (121) with a radial interference fit, and a pair of resetting tabs (130) extending from two ends of the C-shaped annular portion (129), respectively.
 24. The lash adjuster of claim 23 wherein the C-shaped annular portion (129) is corrugated in the axial direction.
 25. The lash adjuster of claim 19 wherein the conical coil spring (123) has a large-diameter end, and includes a resetting tab (124) radially outwardly extending from the large-diameter end.
 26. The lash adjuster of claim 20 wherein the cylindrical coil spring (126) includes a resetting tab (127) radially outwardly extending from one end thereof.
 27. The lash adjuster of claim 24 wherein the resetting tab (130) extending from one end of the C-shaped annular portion (129) crosses the resetting tab (130) extending from the other end of the C-shaped annular portion (129). 28-30. (canceled) 